1. Field of the Invention
The present invention relates to a liquid substance supply device for a vaporizing system which vaporizes a liquid substance such as a liquid organometal or an organometal solution or the like, and also relates to a vaporizer and to a vaporization performance appraisal method.
2. Description of the Related Art
The MOCVD (Metal Organic Chemical Vapor Deposition) method is known as one thin film deposition method in semiconductor device manufacturing processes. In recent years this MOCVD method is rapidly coming into widespread use, since the resulting film quality and the speed of film deposition and step coverage and so on are superior by comparison to spattering methods and the like. There are various methods of supplying the CVD gas which is used in MOCVD devices, such as the bubbling method and the sublimation method. In recent years, the method of supplying a liquid substance that is a liquid organometal or an organometal dissolved in an organic solvent and vaporizing it directly before the CVD reactor has become recognized as an excellent method from the point of view of controllability and stability. In such a vaporization method, a liquid substance is supplied to a vaporizer by a liquid substance supply device, and, in the vaporizer, the liquid substance is sprayed from a nozzle into a vaporization chamber which is maintained at a high temperature, and is thus vaporized.
However, the liquid substance which is used in such a MOCVD method can easily undergo hydrolytic reactions, and there has been a danger that its nature may change due to precipitates being formed in the liquid or the like. Such generation of precipitates can easily lead to problems with the operation of valves provided in the liquid supply lines, or the occurrence of residues within the vaporizer or blockages due to the precipitates or the like. As a result there have been the problems that the rate of flow may become less stable and consistent, and that, if the residues form into particles which arrive at the CVD reactor, the consistency of film deposition may be deteriorated.
In the past, a mass flow controller in which a mass flow meter and a flow amount control valve are combined together has generally been employed for controlling the rate of flow of a liquid substance. If a thermal type mass flow meter is used as the mass flow meter, it can easily be influenced by the ambient temperature, and accordingly it is not desirable to locate such a meter in the vicinity of the vaporizer which attains high temperatures. On the other hand, from the point of view of responsiveness of flow rate control, it is desirable to locate the mass flow controller directly before the vaporizer. As a result there is the problem that, when determining the position in which such a mass flow controller is to be disposed, one or the other of accuracy of flow control and responsiveness must be sacrificed, and accordingly either case causes insufficient installation condition.
Furthermore, when it is not possible to provide a sufficient supply of heat energy to the liquid substance during vaporization, it can happen that non-vaporized residues can be created and can cause blockages in the supply conduits, and there is a danger that the residues can become particulated and can arrived at the CVD reactor and can cause poor film deposition. Yet further, when vaporizing a mixture of a plurality of components, since the vaporization temperatures and the pyrolysis (thermal decomposition) temperature characteristics of the various components are different, it has been easy for residues to be generated by non vaporization or by pyrolysis of some of the components.
Yet further, although it is necessary to appraise the vaporization performance under various conditions of vaporization in order efficiently to implement vaporization while suppressing the generation of non vaporized residues, it is extremely difficult to perform such appraisal due to the characteristics of the substances and so on, and up to the present no established appraisal method has been developed.